Circulation of various fluids in oil and gas wells by various methods is generally dictated by different well conditions. Well circulation is the displacement of fluid from the annulus between the casing and the tubing to the tubing or vice versa for various reasons for displacing the tubing or annulus fluid to increase or lighten the weight of the fluid, performing well treatment, or killing a well by circulation. If a killing mode is desired, communication is provided to expose the well formation to a heavy fluid. For other operations, it is desired to isolate the producing formation from well fluids to prevent formation damage.
Generally, circulation of well fluids is achieved by opening a valve in a sidepocket mandrel or shifting a sliding sleeve valve. These devices have limitations such as a small flow area in the sidepocket of a well mandrel and the short life of the seals on the sliding sleeve type valve. In any event, the prior art devices require a downhole trip to set a plug below the devices in the tubing string when it is desired to prevent completion fluid from entering the formation. This can be difficult and expensive. The present invention is directed to a subsurface well valve such as a circulation valve having a double seat for preventing formation damage and loss of completion fluid to the formation but allowing circulation without the disadvantages of the prior art devices. The present valve provides the advantages of a full flow area substantially equivalent to the flow area in the well conduit or tubing. In one embodiment, a conventional ball type valve may be provided and in another embodiment a flapper valve may be provided which eliminates seals sliding across ports which result in seal damage, but still provides a metal and resilient seat combination on both valve seats.